PG19 Beta3: adapt COPY regressions to psql input draining

[ibrahim halatci (ihalatci)]

Summary

PostgreSQL 19 Beta3 psql commit d6ab88d changed how input is drained after an early server-side COPY rejection. The affected regression tests could consequently consume following SQL as COPY data or otherwise desynchronize their scripts.

• derive an exact PostgreSQL 19 Beta3+ gate from the invoking psql client's VERSION_NUM and VERSION_NAME, including whitespace-suffixed packaged version names
• retain the original COPY commands for PostgreSQL 19 Beta1/Beta2 and PostgreSQL 16-18
• use zero-row \copy ... FROM PROGRAM 'true' only for PG19 Beta3+/RC/final early-failure paths
• preserve all data-bearing COPY semantics and assertions
• use ordinary complete pg_regress alternative expected files; canonical expected files remain byte-for-byte unchanged
• keep the intermediate_results child psql COPY and CREATE as two -c commands in one -1 transaction
• avoid custom launchers, comparators, global normalization, and PG19 Beta3: make COPY failure regressions resilient to psql input draining #8780 files

Affected schedules

• check-multi
• check-multi-1
• check-multi-1-create-citus
• check-enterprise
• check-follower-cluster

Validation

• PostgreSQL 19 Beta3: all touched coverage and all five owning schedules pass (33 / 8 / 194 / 211 / 35)
• PostgreSQL 19 Beta2: all touched coverage and all five owning schedules pass (33 / 8 / 194 / 211 / 35); the validation-only GUC edit was restored byte-for-byte
• PostgreSQL 18.4, 17.10, and 16.14 previously passed all five owning schedules through the byte-identical legacy branch
• the final suffix-only gate broadening changed only the echoed gate line and acceptance of packaged PG19 client names; exact-current-tip local matrix reruns are queued behind the shared fixed-port validation window
• GitHub CI has restarted on the suffix-safe tip and is still running; evaluate its final state before merge

Closes #8781

[ibrahim halatci (ihalatci)]

Release-review blocker: the current end-anchored VERSION_NAME regex rejects valid PG19 clients built with --with-extra-version/packager suffixes (for example 19beta3 (Ubuntu ...) or 19.0 (Debian ...)), selecting the legacy COPY path. A corrective client-version gate and suffix matrix are in progress.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.75%. Comparing base (866ab1b) to head (2d3b915).

Additional details and impacted files

@@               Coverage Diff                @@
##           pg19-support    #8785      +/-   ##
================================================
+ Coverage         88.69%   88.75%   +0.05%     
================================================
  Files               289      289              
  Lines             65062    65065       +3     
  Branches           8200     8201       +1     
================================================
+ Hits              57709    57746      +37     
+ Misses             4984     4955      -29     
+ Partials           2369     2364       -5     

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